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This thesis is concerned with the response of multi-story prestressed concrete frames to seismic loading, and the ductility demands of the constituent members. In that regard, an idealized model for the end moment-plastic rotation relationship of prestressed concrete members was developed based on a published moment-curvature idealization for prestressed concrete. The idealized moment-rotation model, which included stiffness and strength degradation, was used to introduce all post-elastic action In a beam-column element, which consisted of an elastic beam connecting concentrated hinges modeled as nonlinear rotational springs. The subsequent use of the element in the nonlinear analysis of a typical multi-story prestressed concrete frame indicated that both the lateral displacements, and the girder end rotational and hinge curvature ductilities would be somewhat higher for a prestressed concrete frame than for a reinforced concrete frame with the same initial stiffness and strength. As an effort to limit deflections, and minimize member damage under moderate seismic loading the use of a higher base shear for a prestressed concrete structure than for a comparable reinforced concrete structure appears warranted. / Applied Science, Faculty of / Civil Engineering, Department of / Unknown

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Flat-slab buildings designed and detailed for gravity loads only typically do not have the ability to resist moderate earthquakes without experiencing severe damage. The damage potential of such seismically deficient buildings therefore needs to be assessed and strategies developed to improve their seismic resistance. Punching failure at slab-column connections in non-ductile flat-slab buildings during earthquakes can trigger progressive collapse of floor slabs. Based on the test results of a large number of interior and exterior connections, a methodology is developed to predict shear and unbalanced moment-transfer capacities of connections under combined gravity and lateral loads. Furthermore, a frame analysis procedure is developed based on the equivalent frame concept which targets both the moment-transfer capacity as well as stiffness of the interior and exterior slab-column connections. The approach employs a parametric hysteretic model and is based on the effective slab-width concept. The proposed procedure for evaluating the seismic capacity of flat-slab connections and frames is verified by comparing the calculated and measured responses of two-bay flat-slab subassemblies tested under earthquake-type loading. Seismic reliability against punching failure of slab-column connections in flat-slab buildings designed for gravity loads was investigated using the proposed equivalent frame approach. The reliability analysis indicated that the flat-slab buildings constructed prior to the 1960's could experience significant damage during moderate intensity earthquakes. By limiting the gravity load on floor slabs and by controlling the lateral drift, the potential for punching failure in flat-slab buildings can be minimized. The seismic resistance of older flat-slab buildings can be improved by retrofitting interior connections to protect against progressive collapse and by utilizing infill walls to control lateral drift. An economical connection retrofit scheme is proposed and verified experimentally. The equivalent strut concept is used to model masonry infills whose effectiveness in controlling the lateral drift is demonstrated through theoretical analysis of typical flat-slab frames.

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No description available.

Recent geologic research has shown that earthquakes more destructive than formerly expected are likely to occur in the Pacific Northwest. To mitigate catastrophic loss, planners are gathering information to make decision on implementing regional seismic retrofit programs. This research develops a model to estimate regional earthquake losses for existing buildings, and determine optimal retrofit priorities and budgets. Fragility curves are developed to provide earthquake damage estimates for a range of seismic intensities. The published earthquake damage estimates of a large group of prominent earthquake engineering experts are extended to include the combined effect of structure type, earthquake-sensitive variations in building design, site-specific soil conditions, and local seismic design practice. Building inventory data from a rapid visual screening survey of individual buildings form the basis for modeling structural variations. Earthquake Hazard Maps are the basis of modeling the effect on building damage of ground motion amplification, soil liquefaction, and slope instability. Published retrofit effectiveness estimates and retrofit cost data are used to estimate post-retrofit damage avoided, lives saved, and retrofit cost. A Building Classification System is formulated to aggregate buildings with similar retrofit benefit magnitudes. A cost-benefit analysis is used as the basis for a retrofit prioritization and efficiency analysis, to establish the cut-off point for an optimal retrofit program. Results from an Expected Value and a Scenario Earthquake Event are compared. Regional Earthquake Loss and Retrofit Analysis Program (REAL-RAP) software was developed, and used to make a loss estimate for more than 7,500 buildings inventoried in the 1993 Portland Seismic Hazards Survey. One hundred percent of the loss of life is attributed to only 10-percent of the buildings. A retrofit analysis is made for a Design Basis Earthquake. Twelve-percent of the building inventory was identified for the optimal retrofit program, wherein 98-percent of the loss of life is avoided at less than one-quarter the cost of retrofitting all the buildings. An alternate optimal retrofit program was determined using an Expected Value Analysis. Most of the buildings in the Design Basis Earthquake optimal retrofit program are also contained in the alternate program.

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Base isolation is an alternative seismic design strategy in which the primary structures and their internal components are uncoupled from the potentially damaging horizontal components of an earthquake by base isolators which attenuate the transmission of horizontal acceleration into the system. Rotating machines are among the key internal components of many modern structures. In this study, flexible rotating machines protected against seismic excitations by two particular types of base isolation systems, Resilient-Friction Base Isolation (R-FBI) and Laminated Rubber Bearing (LRB), are investigated. A comparative study is carried out to compare aseismic responses of base isolation systems and their corresponding fixed-base ones in protecting a rotating machine rigidly attached to a floor level or independently isolated. Finite-element analysis techniques based on energy methods are proposed to investigate a general complex model of the rotating system which incorporates nonuniform properties as well as one or more rigid disks along the length of the flexible shaft and complicated bearing support systems. The equations of motion for the rotating machines using these methods are developed. An approximate linear analysis to gain insight into the behavior of a simple linear two-degree-of-freedom isolated structure is presented. This elementary analysis allows us to develop an analytical expression for the fundamental frequencies, and their corresponding mode shapes, amplification factors and design response spectra of base shear. It also demonstrates that the transmission of ground motion to the systems is effectively controlled through the isolation of the system at its base. The combined rotating machine-isolator; rotating machine-structure-isolator; and structure-isolator systems, and their corresponding fixed-base ones are investigated and compared. The governing equations of motion and the criteria of phase transition (R-FBI only) are presented. Parametric studies to examine the sample response and response spectra, as well as effects of variations in some system properties including friction coefficient, damping ratio, mass ratio, ground motion excitation intensity, shaft flexibility, bearing rigidity and rotating speed, on the response of these systems are performed. The peak accelerations and relative displacements of the base isolated systems and corresponding fix-base ones are analyzed and compared. Other response quantities of special interest such as sliding displacement, residual displacement, cumulative displacement and relative-to-ground displacement of the structure are also evaluated. Based on the numerical results, conclusions of the effectiveness of the R-FBI and LRB systems in protecting the rotating machines and the structures are made. / Graduation date: 1998